Anthropic shipped "mods" for Claude Code (released Oct 1), small add-ons that change how Claude Code itself looks and works by listening to events and watching, modifying, or handling them. The video walks through nine mods worth trying — Savvy Progress, Claude Skins, You Should Know, File Tree, Cache Tax, Blast Radius, Reflect, Terminal Browser and Replay Theater — and explains how mods differ from skills and MCP connectors. Building one is just a matter of describing it to Claude, which has a built-in "plugin authoring" skill; mods are temporary by default until you ask Claude to save them as an installed plugin.
- Mods differ from skills and connectors: a skill tells Claude how to do a job and a connector plugs Claude into another app, while a mod runs inside Claude Code and changes the interface itself — extra buttons, side panels, even a minigame.
- Mods work in the Claude Code terminal and the desktop app's code tab, but were not yet available in the VS Code extension at recording time; you need version 2.1.287 or newer.
- Technically, Claude Code emits an "event" whenever it does something, and a mod is code that listens for those events and can watch, change, or handle them — Savvy Progress uses all three to draw a progress bar and a live sub-agent panel showing model, progress and API cost.
- Cache Tax targets wasted spend: the prompt cache goes cold after roughly an hour on a normal subscription, forcing Claude to reread the whole conversation, so the mod estimates that cost before you send and offers a /keepwarm command that pings the session before the cache expires.
- Blast Radius, built by Anthropic, intercepts risky commands like deleting a folder, lists exactly which files would be removed and requires a human to press proceed — a response to real cases where frontier models wiped entire projects.
- Reflect acts like micro-scale RLHF: when you type feedback with trigger words like "no" or "I wish we'd done it this way," a banner offers to save that correction as a permanent rule in your CLAUDE.md or skill file.
- Most mods run on deterministic code and cost no extra tokens, but ones like "You Should Know" run a second agent in the background and draw on your normal Claude usage.
- Several mods are useful outside coding — File Tree can track which tax documents Claude opened and changed, and Replay Theater can step through edits Claude made to an article draft.
It's the clearest explanation of the underlying mechanism, which makes every other mod in the list make sense.
Every time Claude does something like running a command, Claude Code actually sends out a little signal called an event. And a mod is just a small piece of code that listens for those events so that when one comes through, the mod can do one of three things. It can watch that event, it can change it, or it can handle it itself.
A concrete, money-saving explanation of prompt caching plus the /keepwarm trick that most users won't know about.
After a while, usually about an hour on a normal Claude subscription, it goes cold. And once that prompt cache is cold, the next prompt that you send actually makes Claude reread your entire conversation, which can really eat into your usage limits.
If you can describe a feature that you wish Claude Code had, it can now build that feature into itself.
You might not think that your agent would ever delete your files, but I've seen so many edge cases already where even a smart frontier model would wipe out someone's entire project.
A mod that Claude builds for you is temporary by default. So when you find one that you like, ask Claude to save it as a plugin and install it.